This invention relates to digital watermarking of multimedia data for copyright protection.
Digital watermarking is a process of embedding information, sometimes referred to as a signature, directly into the media data by making small modifications to the data. The subsequent extraction of the signature from the watermarked media data may be used to identify the rightful owner, the intended recipients, and the authenticity of a media data. Because of the rapid growth of digital imagery, the increasingly easy access to digital media, and the availability of powerful digital image manipulation tools, media security has become an important issue. Digital watermarks have been proposed as a method for indicating copyright ownership of multimedia data.
There are two requirements for invisible watermarks: First, the watermarks should be perceptually invisible, i.e., they should not interfere with the media being protected; Second, the watermark should be sufficiently robust to defeat any attempt to eliminate the watermark, or to forge a fake watermark to establish a counterfeit ownership claim. They should also be sufficiently robust to withstand common signal processing. Particularly, a watermark should be detectable even if common signal processing operations have been applied to the watermarked image.
Early developments in digital watermarking concentrated on the first objective without considering the second, resulting in xe2x80x9cinvisiblexe2x80x9d watermarks which are easily circumvented. Recently, work has been devoted to designing robust watermarking schemes. Perceptual models have been incorporated to equalize watermark qualities of perceptual invisibility and robustness to signal processing. In some applications, it may be advantageous to exploit the human visual system""s superior ability to recognize a correlated pattern. However, in the prior art, instead of directly extracting a watermark image, the superior recognition ability of the human visual system is only used to visualize some detection results.
Previous methods suffer from one or some of the following drawbacks. They are not generally robust to signal processing The watermarks are embedded to the visually least significant portion of an image. While this approach results in watermarked images with very good visual quality, the embedded watermark is generally vulnerable to signal processing, such as JPEG compression, lowpass filtering etc.
The original un-watermarked image is needed in the detection process. Some previous methods use the original un-watermarked image in the watermark detection process. Typically the watermark sequence may be first extracted by subtracting the original image data from the test (potentially watermarked) image data. While this generally increases the detection capability of the watermarking system, and is helpful for some applications, such as identifying an illegal distributor, it is not applicable to resolving rightful ownership claim. This is because the authenticity of the claimed xe2x80x9coriginalxe2x80x9d image is still questionable. An attacker may forge a fake xe2x80x9coriginalxe2x80x9d image and a fake watermark and come up with a counterfeit ownership claim. Requiring the watermark to be dependent on the xe2x80x9coriginalxe2x80x9d image in the hope that with this constraint the xe2x80x9coriginalxe2x80x9d image may not be generated after the fake watermarks does not necessarily resolve this problem, because an attacker still has the flexibility to manipulate the claimed xe2x80x9coriginalxe2x80x9d image to computationally search for an original-image-dependent fake watermark, which has certain correlation with the extracted watermarks.
The detector output is not immediately obvious to a jury. Some schemes embed some potentially registered numbers such as an owner ID, or image ID, similar to the ISBN # of a book. The physical meaning of the extracted bits has to be conveyed by an interpreter such as a central registration agent, or a technical expert in the court, which may not be straightforward to a jury. In addition, the number of bits that may be embedded and later reliably extracted depends on how severely the watermarked image has been processed. One has to determine the tradeoff between number of bits embedded and the robustness of the watermark to signal processing at the time of watermark insertion. A one bit error in the extracted bits may cause the whole ID number to be invalid. Some methods are known which embed a binary image, and hence are easier for a jury to understand, however, such techniques still have to use the original image in the watermark extraction process, thus are not applicable to resolving rightful ownership as discussed above. Furthermore, such methods do not allow the watermark detector to adaptively choose the tradeoff between the degree of robustness and the resolution of the extracted watermark
In this invention, a method to xe2x80x9cvisualizexe2x80x9d, in an adaptive manner, the invisible watermarks for proving the ownership is described. A method which is capable of embedding a good resolution meaningful binary watermark image in an image and later extracting different versions of that watermark image with varying resolutions is proposed. The method has the nice feature that the watermark detector is allowed to adaptively choose the trade-off between robustness degree and resolution of the extracted watermark image.
A meaningful binary watermark image is embedded and extracted, which will greatly facilitate the process of convincing a jury of an ownership claim. While a statistical technique which may quantify the false alarm detection probability should be considered as a fundamental measure for a valid ownership claim, the ability to extract a meaningful watermark image, i.e., a logo, a registration number, or an image recognizable by a lay person, will greatly facilitate the process of convincing a jury of an ownership claim. A jury usually consists of nontechnical people. The presentation of an extracted meaningful watermark image is much more convincing than a numerical value.
A method for embedding and extracting visually imperceptible indicia in an image includes embedding a visually imperceptible indicia in an original image; testing a test image for an embedded visually imperceptible indica; and extracting the visually imperceptible indicia from the test image to determine if the test image is a copy of the original image. The method may also include examining segments of varying sizes in the image at the decoder for detecting each bit of the embedded signature, and allows a user of the method of the invention to select trade-offs between resolution and detection performance, and to select an overall level of performance.
An object of the invention is to provide a valid, robust watermarking method which will facilitate the process of convincing a jury of an ownership claim.